This is so good! This pie needs to chill about 8 hours before serving so make the day before or early in the day. Adapted from Southern Living Annual Recipes 2005. Chilling time is not included in the cook or prep time.
Heat milk in a 3 quart saucepan over medium heat until it begins to bubble around the edges (DO NOT BOIL).
Remove from heat and whisk in the chocolate morsels until melted.
Stir together cold water and cornstarch until dissolved.
Whisk cornstarch mixture, sweetened condensed milk, eggs, and vanilla into chocolate mixture. Bring to a boil over medium heat, whisking constantly. Boil 1 minute or until mixture thickens and is smooth. Be careful not to overcook.
Remove from heat and whisk in butter.
Spoon mixture into pie crust.
Cover and chill at least 8 hours.
Beat whipping cream at high speed with a mixer until foamy. Gradually add sugar and beat until soft peaks form.